T cell dysfunction contributes to the susceptibility of patients with the Wiskott-Aldrich syndrome (WAS) to infection, autoimmunity and lymphoid malignancy. This project probes the function of WASP and its partner WASP interacting protein WIP in T cells. Most of WASP is complexed with WIP in T cells. WASP levels of drop to ~10% of normal in T cells from WIP KO mice and from WAS patients with mutations that disrupt WIP binding, suggesting that WIP stabilizes WASP. Our Preliminary data show that the hierarchy of T cell dysfunction is WASP/WIP DKOWIP KOWASP KO, bearing in mind that since WASP levels are low in WIP KO T cells the individual contribution of WIP to the WIP KO phenotype is unknown. Our overall hypothesis is that WIP and WASP function in T cells both as a complex and independently. To test our hypothesis we propose to use genetically engineered mice which selectively lack WIP, WASP or both, or in which the WASP/WIP complex is disrupted. We will: 1. Compare T cells from WASP/WIP DKO mice to T cells from WT mice to define the combined role of WIP and WASP. In addition, comparison with WASP KO T cells would define WIP functions that may be independent of WASP. 2. Reconstitute T cells from WIP KO mice with a peptide that consists of the WASP binding domain (WBD) of WIP in order to restore WASP levels, and thus generate WIP deficient/WASP expressing T cells. We will compare T cells from these mice to WT T cells to define the role of WIP. 3. Disrupt the WASP/WIP complex expressing the WBD in WT T cells to test the hypothesis that there is a subset of signaling functions that is dependent on the WASP/WIP complex. 4. Examine the structure and function of T cells from knockin mice that express a WIP mutant that lacks the actin-binding region to define the role of WIP binding to actin in the subcellular localization and function of the WASP/WIP complex. The results of the proposed experiments in the mouse will aid in our understanding of the pathogenesis of WAS in humans and should lead to novel treatments for this disease.